Engine cooling fan

ABSTRACT

An engine cooling fan ( 100 ) comprising a hub ( 102 ) and a plurality of blades ( 104 ) each of which extends away from the hub ( 102 ), wherein the hub ( 102 ) defines a rotation axis about which the hub ( 102 ) is adapted to rotate during operation; wherein each blade ( 104 ) defines an attachment part ( 108 ), an air moving part ( 106 ), and a center line extending in a longitudinal direction of the blade ( 104 ) between a tip end and a hub end of the blade; wherein at least a first zone of the center line extends in a direction transverse to a normal of the rotation axis of the hub ( 102 ). Moreover the present invention relates to a blade ( 104 ) for use in the fan ( 100 ) and a kit comprising the blade ( 104 ) and the fan ( 100 ).

FIELD OF THE INVENTION

The present invention relates to an engine cooling fan with a hub and a plurality of blades. In particular the present invention relates to an engine cooling fan wherein a center line of at least a part of the blade extends in direction transverse to a normal of an axis of rotation of the hub. Furthermore, the present invention relates to a blade for an engine cooling fan. Moreover, the present invention relates to a kit comprising a hub and a plurality of blades.

BACKGROUND OF THE INVENTION

In relation to engine cooling fans is it a known problem that with an increasing rotational speed, an increased deflection of the blades is experienced. This causes the problem that the structure into which the cooling fan is build must provide enough clearance to allow the blades to deflect such that the fan is not prevented from rotating due to the deflecting blades blocking the rotation.

It is an object of the present invention to provide an engine cooling fan where the blades do not deflect in a direction parallel to an axis of rotation of the hub of the fan.

DESCRIPTION OF THE INVENTION

In a FIRST aspect the present invention relates to an engine cooling fan comprising a hub and a plurality of blades each of which extends away from the hub, wherein the hub defines a rotation axis about which the hub is adapted to rotate during operation; wherein each blade defines an attachment part, an air moving part, and a center line extending in a longitudinal direction of the blade between a tip end and a hub end of the blade; and wherein at least a first part of the center line extends in a direction transverse to a normal of the rotation axis of the hub.

In the context of the present invention, the term ‘engine cooling fan’ shall be understood as any fan which is suitable for cooling an engine, either by cooling a radiator which is used to cool a cooling medium that is circulated between the radiator and the engine and/or by cooling the engine directly.

The hub will typically be adapted to be connected or fastened to an axle which is rotated so as to cause the fan to rotate. This axle may be an axle which forms an extension of the axle of the engine.

Each blade is connected to the hub either directly of by means of one or more elements interconnecting the blade and the hub. In one embodiment, the blades and the hub form a unitary element. In the context of the present invention, the term ‘unitary element’ shall be understood such the parts constituting the unitary element are formed as or joined into one single entity. In one embodiment, the unitary element is a monolithic element. In the context to the present invention the term ‘monolithic element’ shall be understood as an element which is formed into one entity without defining any seams e.g. welding or moulding seams.

In another embodiment, the blades are releasably and reattachably attached to the hub. In one embodiment, the hub and the blades are designed such that the pitch of the blade may be set in connection with the attachment of the blade to the hub. In this embodiment, the pitch of the blades may be changed by disconnecting the blades from the hub and subsequently attaching the blades to the hub—however at a new pitch angle.

The hub and/or the blade may comprise a metal material or a plastic material or a fibre glass. Examples are iron, aluminium, polycarbonate, polystyrene, polytetrafluoroethylene, polyamid and polypropolene. It will be appreciated that any other metal or plastic material may be used.

The fan comprises a plurality of blades such as four, five, six, seven, eight, nine, ten, eleven, twelve, thirteen, fourteen etc. The blades will typically be equidistantly spaced apart circumferentially. The length of the blades may be in the range 200-2000 milimeters, such as 500 milimeters, such as 1000 milimeters, such as 1500 milimeters, such as 2000 milimeters.

Each blade defines an attachment part and an air moving. In embodiments, where the blades are detachably and/or re-attachably attached to the hub, the attachment part is that part of the blade which is attached to the hub. In embodiments where the blades and the hub form a unitary element, the attachment part shall be construed as the transition between the blade and the hub.

The center line of the blade may define one or more zones in the longitudinal direction of the blade. E.g. a first zone of that part of the center line which extends through the air moving part of the blade may extend non-parallel to a normal of the rotation axis of the hub, i.e. in a direction transverse to this normal. Moreover, the center line may define a second zone which coincides with the normal.

In one embodiment, the second zone is positioned closer to the hub end of the blade than the first zone. In another embodiment, the first zone is positioned closer to the hub of the blade than the second zone.

Each blade defines a center line which extends between the tip end and the hub end of the blade. In one embodiment, the center line extends through a geometrical center of any cross-section of the air moving part which is orthogonal to the centre line. In one embodiment, the center line extends through the geometrical center of any cross-section of the blade or the air moving part thereof, which is parallel to the rotational axis of the fan. In another embodiment, the center line extends through the geometrical center of any cross-section of the blade or the air moving part thereof, which is orthogonal to a line extending through a normal of the rotational axis of the fan i.e. this line defines a normal to the cross-section. In one embodiment, the center line extends through a geometrical center of any cross-section of the blade which defines a normal to the centre line.

In order to prevent the blade from moving in a direction parallel to an axis of rotation of the hub of the fan, the air moving part of the blade may be designed such that for any point on that part of the center line which extends through the air moving part, the resulting vector of all forces acting on the point defines a tangent to the respective position. This is achieved by providing an air moving part with a curved center line. It will be appreciated that during rotation at least a centrifugal force and a lift force will act on the blade. The numeric value of these two forces raise with the same rate (as a function of the rotational velocity of the fan). Thus for any rotational speed, the resulting force will define a tangent to the center line in the respective point, whereby the blade is prevented from deflecting during use.

It will be appreciated that by designing the blade such that the resulting vector of all forces acting on the point defines a tangent to the center line in the respective position it is achieved that no forces act on the point in a direction transverse to the tangent. Accordingly, the resulting force vector is in the direction of the center line. It will be appreciated that it is relatively easy to design the blade such that even large tensile forces will cause minimal elongation of the blade (in the direction of the center line). In contrast hereto even small bending moments (e.g. created by the lift of generated when air flows past the blade during rotation of the fan) will cause the blade to deflect. Thus by designing the blade such that the resulting force is not transverse to the longitudinal direction of the blade, the blade is prevented from deflecting.

In the context of the present invention the term ‘centrifugal force’ shall represent the effects of inertia that arise in connection with rotation and which are experienced as an outward force away from the axis of rotation. Moreover, the term ‘lift’ shall be understood as the perpendicular component of a force which is generated by a fluid flowing past. The perpendicular component being perpendicular to the oncoming flow direction of the fluid.

It will be appreciated that the blade may be linear thus having a linear center line. In other embodiments, the blade is curved whereby the center line is curved such that it defines at least one concavity. In another embodiment, a blade defines a curved part and a linear part, thus with curved and linear center lines, respectively.

It will be appreciated that the wider each blade is in the vicinity of the hub (i.e. the larger an angular sector it covers), the fewer blades may be positioned along the circumference of the hub. Thus in order to allow for a large number of blades to be positioned along the circumference of the hub, the blades may be designed such that the angle defined between rotational axis of the fan and a chord line of the blade (which extends through both the leading edge and the trailing edge of the blade) is significantly different from 90 degrees. In other words, the pitch in the area of the hub may be as large as possible while at the same time ensuring that the blade has the desired aerodynamic properties.

In one embodiment, the first derivative of the pitch in the hub end is larger than the first derivative of the pitch in the tip end. Moreover, the second derivative of the pitch in the hub end may be larger than the second derivative of the pitch in the tip end.

In the context of the present invention, the term ‘pitch’ shall be understood as the angle defined between the plane of rotation of the blade and the profile chord of the blade, the profile chord being a defined as a line extending through the leading edge and the trailing edge of the blade, and the plane of rotation having the rotational axis as a normal.

In the context of the present invention, the term ‘the first derivative of the pitch’ shall be understood as the rate of change of the pitch in the area of a chosen point, relative to the longitudinal direction of the center line. Similarly, the term ‘the second derivative of the pitch’ shall be understood as the rate of change of the first derivative of the pitch, relative to the longitudinal direction of the center line.

Moreover, the first derivative of the pitch may decrease in the direction of the tip end. As an example, the first derivative of the pitch may be 10 percent larger in the hub zone than in the tip zone, such as 15 percent larger, such as 20 percent larger, such as 25 percent larger, such as 30 percent larger, such as 50 percent larger.

In one embodiment, a width of each blade (defined between a leading edge and a trailing edge of the blade) in the tip zone is larger than the distance between the hub ends of two neighbouring blades

In another embodiment, wherein a width of each blade (defined between a leading edge and a trailing edge of the blade) in the hub zone is larger than the distance between the hub ends of two neighbouring blades.

In a SECOND aspect, the present invention relates to a blade for an engine cooling fan, the blade being according to invention according to the first aspect.

The invention according to the second aspect may comprise any combination of features and/or elements of the invention according to the first aspect.

In a THIRD aspect, the present invention relates to a kit comprising a hub and a plurality of blades according to invention according to the first aspect.

The invention according to the third aspect may comprise any combination of features and/or elements of the invention according to the first aspect.

BRIEF DESCRIPTION OF THE FIGURE

FIG. 1 discloses a front elevational view of the fan,

FIG. 2 discloses a side view of the fan,

FIG. 3 discloses an isometric view of the fan,

FIG. 4 discloses a front elevational view of the blade from a first side,

FIG. 5 discloses a side view of the blade,

FIG. 6 discloses a front elevational view of the blade from a second side,

FIG. 7 discloses an end view of the blade seen from the hub end towards the tip end,

FIG. 8 discloses an end view of the blade seen from the tip end towards the hub end, and

FIG. 9 discloses the forces acting on each of the blades during rotation of the fan.

DETAILED DESCRIPTION OF THE FIGURES

FIGS. 1-3 disclose an engine cooling fan 100 according to the present invention. The fan comprises a hub 102 and a plurality of blades 104 which extend radially from the hub 102. In the embodiment of FIGS. 1-3, the fan comprises twelve blades 104 which are spaced apart equidistantly along the circumference of the hub 102. Each blade defines an air moving part 106 and an attachment part 108, see FIG. 4. The air moving part 106 is designed such that when the engine cooling fan 100 is rotated as indicated by arrow 110, a flow of air is generated as indicated by arrow 112.

The width of the air moving part 106 of each blade—in the area of the hub—is wider than the distance between two neighbouring attachment parts. Thus in order to make it possible to arrange the blades, the chord of the blades extend in a direction which is transverse to a plane relative to which the rotational axis defines a normal.

This may also be seen when looking on the pitch of different points of the blade. Accordingly, the pitch per distance (i.e. the first derivative of the pitch) between the reference lines 114 and 118 is smaller than the pitch per distance between the reference points 116 and 118.

This is exemplified in the following example:

The distance between the lines 114 and 118 may in the example be 0.352 meter while the relative pitch between the two lines is 24 degrees. At the same time the distance between the lines 116 and 118 may be 0.0922 meters, while the relative pitch between the lines is 14.3 degrees. Accordingly, the pitch per distance between the lines 114 and 118 is 24 degrees divided by 0.352 meter i.e. 68 degrees per meter. At the same time the pitch between the lines 116 and 118 is 14.3 degrees divided by 0.0922 meters i.e. 155 degrees per meter. Accordingly, the first derivative of the hub zone (the hub zone being defined between the lines 116 and 118) is larger than in the tip zone (the tip zone being defined between lines 118 and 114).

In order to prohibit the blade from deflecting during use, the air moving part 106 of the blade is curved such that the center line of the blade (not illustrated) does not coincide with a radial line 120 (which defines a right angle with the rotational axis of the fan). In FIG. 9 this is evident from the fact that the blade is curved in a direction away from the radial line 120. It will be appreciated that FIG. 9 discloses a cross-section through the center line of the blade. The cross-section being in the longitudinal direction of the blade.

The curve of the blade is chosen such that for any position on the center line, the resulting vector 122 at any point along the center line of all forces acting on the point defines a tangent 124 to the respective point on the center line. In FIG. 9 two forces acts on the blade, namely the centrifugal force 126 and the aerodynamic force 128.

As the resulting force defines a tangent to the point, the only effect of the resulting force is an insignificant elongation of the blade due to the resulting force being a tensile force.

The curve of the blade may also be seen in FIG. 8, where the distance 130 indicates the distance between the center line at the tip of the blade and the radial line 120. 

1. An engine cooling fan comprising a hub and a plurality of blades each of which extends away from the hub, wherein the hub defines a rotation axis about which the hub is adapted to rotate during operation; wherein each blade defines an attachment part, an air moving part, and a center line extending in a longitudinal direction of the blade between a tip end and a hub end of the blade; wherein at least a first zone of the center line extends in a direction transverse to a normal of the rotation axis of the hub, and wherein the center line extends through a geometrical center of any cross-section of the air moving part which is orthogonal to the centre line.
 2. The engine cooling fan according to claim 1, wherein a second zone of the center line coincides with the normal.
 3. The engine cooling fan according to claim 2, the second zone is positioned closer to the hub end of the blade than the zone part.
 4. The engine cooling fan according to claim 1, wherein the center line extends through a geometrical center of any cross-section of the blade which defines a normal to the centre line.
 5. The engine cooling fan according to claim 1, wherein the air moving part of the blade is designed such that for any point on that part of the center line which extends through the air moving part, the resulting vector of all forces acting on the point defines a tangent to the respective point.
 6. The engine cooling fan according to claim 1, wherein the blade is designed such that for any point on the center line, the resulting vector, in a plane defined by the center line of the blade and the rotation axis of the hub, of all forces acting on the point defines a tangent to the respective point.
 7. The engine cooling fan according to claim 1, wherein the center line is curved such that it defines at least one concavity.
 8. The engine cooling fan according to claim 1, wherein the first derivative of the pitch in the hub end is larger than the first derivative of the pitch in the tip end.
 9. The engine cooling fan according to claim 1, wherein the second derivative of the pitch in the hub end is larger than the second derivative of the pitch in the tip end.
 10. The engine cooling fan according to claim 1, wherein the pitch decreases in the direction of the tip end.
 11. The engine cooling fan according to claim 1, wherein the first derivative of the pitch is 10 percent larger in a hub zone than in a tip zone.
 12. The engine cooling fan according to claim 11, wherein a width of each blade is defined between a leading edge and a trailing edge of the blade, and wherein the width of the blade in the tip zone is larger than the distance between the hub ends of two neighbouring blades.
 13. The engine cooling fan according to claim 11, wherein a width of each blade is defined between a leading edge and a trailing edge of the blade, and wherein the width of the blade in the hub zone is larger than the distance between the hub ends of two neighbouring blades.
 14. The blade for an engine cooling fan, according to claim
 1. 15. The kit comprising a hub and a plurality of blades according to claim
 1. 